Background:Many studies have investigated tricuspid annular plane systolic excursion (TAPSE) as a longitudinal right ventricular (RV) contraction. The aim of this study was to clarify the mechanism of RV systolic function compared with longitudinal and radial RV contractions in healthy children.Methods and Results:A total of 815 consecutive healthy children and adolescents were enrolled. We measured TAPSE on M-mode echocardiography as a longitudinal RV contraction. RV wall displacement (RVWD) toward the center of the left ventricle (LV) was measured in the short-axis view on M-mode echocardiography. RV stroke volume (RVSV) was obtained using pulse Doppler echocardiography as an indicator of RV global systolic function. RVSV and TAPSE had a positive but non-linear correlation with a definite inflection point around 15 mm of TAPSE. Subjects were stratified into 2 groups according to TAPSE (≤15 mm or >15 mm). In subjects with TAPSE ≤15 mm, RVWD and TAPSE were identified as independent predictors of RVSV. In contrast, in subjects with TAPSE >15 mm, TAPSE were identified as an independent predictor of RVSV.Conclusions:Normal RV contraction pattern shifts from radial to longitudinal directions at approximately 15 mm of TAPSE. RVSV is primarily generated by longitudinal contraction, but in neonates, RVSV is supported not only by longitudinal contraction but also by radial contraction. (Circ J 2014; 78: 1967–1973)